1. Technical Field
This invention relates to an image forming apparatus, such as a copier, a printer, a facsimile machine, a multifunctional machine combining multiple functions of these devices, etc., and in particular to a ventilation structure used in the image forming apparatus.
2. Related Art
A fixing device is generally provided in an electro-photographic image forming apparatus, such as a copier, a printer, a facsimile machine, a multi-functional machine combining multiple functions of these devices, etc., to melt and fix toner (i.e., developer) onto a recording medium.
The fixing device generally includes a fixing roller as a fixing member to fix an image onto a recording medium and a pressure roller opposed to the fixing roller as an opposed member to form a fixing nip therebetween. A heater is disposed in the fixing roller. The pressure roller contacts the fixing roller with a prescribed pressure and forms the fixing nip at a pressure contact section, in which the pressure roller and the fixing roller mutually contact each other.
In recent years, image forming apparatuses capable of executing high-speed processing are in demand. However, in such a high speed machine, as line speed and/or a sheet thickness increase, the amount of heat emitted by the fixing device also increases and greatly contributes to an increase in temperature inside the apparatus, which is undesirable because the precision of a temperature detector such as a thermopile or the like disposed in the fixing device to control the temperature of the fixing roller is degraded by exposure to high temperatures, as is the performance of a belt cleaner disposed close to the fixing device.
Conventionally, a system to prevent such a rise in temperature of the temperature detector as described in JP-2001-228742-A is known.
Specifically, as described in JP-2001-228742-A, a temperature detector is attached to a frame of an apparatus body opposed to a fixing cover covering a fixing device at a prescribed distance. The system of JP-2001-228742-A is thus designed to let air flow into a space formed between the frame of the apparatus body and the fixing cover. That is, by blowing air into the space and thereby preventing a rise in temperature of the temperature detector, thereby maintaining accurate temperature detection by the temperature detector.
However, with the above-described system of JP-2001-228742-A, although air flows around the temperature detector to prevent a rise in temperature of the temperature detector, the airflow does not reach the belt cleaner and thus a rise in temperature of the belt cleaner is not prevented. Moreover, since the air simply flows, cooling is generally insufficient.
Further, because a thermopile is categorized into a non-contact type temperature detector, a surface of a temperature detection element of the thermopile needs to directly face a temperature detection object. Specifically, any object is inhibited to intervene a space between the fixing roller and the thermopile, while the thermopile needs to avoid exposure of its own.
Since the fixing roller is used in high temperature environment at about 180 degree Celsius, silicone oil included in the fixing roller volatiles as a result. In the past, however, no counter measure is taken against contamination of the surface of the detection element caused by the volatile gas emitted from the fixing roller.
When the surface of the detection element of the detector is contaminated by the volatile gas, temperature detection cannot be accurate.